Wireless networks have experienced increased development in the past decade. Two types of wireless networks are infrastructure-based wireless networks, and ad hoc wireless networks.
An infrastructure-based wireless network typically includes a communication network with fixed and wired gateways. Many infrastructure-based wireless networks employ a mobile unit which communicates with a fixed base station that is coupled to a wired network. The mobile unit can move geographically while it is communicating over a wireless link to the fixed base station. When the mobile unit moves out of range of one base station, it may connect or perform a “handover” to a new base station and continue communicating with the wired network through the new base station.
In comparison to infrastructure-based wireless networks, such as cellular networks or satellite networks, ad hoc networks are self-forming networks which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc network is formed entirely of mobile nodes. An ad hoc network can, for example, refer to a local area network (LAN) or other small network, especially one with wireless or temporary plug-in connections, in which some of the network devices are part of the network only for the duration of a communications session or, in the case of mobile or portable devices, while in some close proximity to the rest of the network. An ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network. Because the topology of an ad hoc network can change significantly techniques are needed which can allow the ad hoc network to dynamically adjust to these changes. Due to the lack of a central controller, many network-controlling functions can be distributed among the nodes such that the nodes can self-organize and reconfigure in response to topology changes.
Each node can typically directly communicate over a short range with nodes (sometimes referred to as “neighbor nodes.”) which are a single “hop” away. When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“hop-by-hop”) until the packets reach the destination node. Each intermediate node acts as a router which can intelligently route the packets (e.g., data and control information) to another node until the packets eventually reach their final destination. As used herein, “a router” could be either a layer 2 or a layer 3 device, (e.g., generic routing functionality), not specific to an Internet Protocol (IP) implementation or a specific Media Access Control (MAC) implementation. Layer 2 refers to the data link layer of the Open Systems Interconnection (OSI) communication model. The data link layer is concerned with moving data across the physical links in the network. In the context of the IEEE-802 LAN standards, the data link layer contains two sublayers called the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer. The data link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. The data link layer also ensures that incoming data has been received successfully by analyzing bit patterns at special places in the frames. In a local area network (LAN) or other network, the Media Access Control (MAC) address is a host computer's unique hardware number. On an Ethernet LAN, the MAC address is an Ethernet address. When a computer or other host connects to the Internet, a correspondence table relates the hosts IP address to the host's physical (MAC) address on the LAN. The MAC address is used by the Media Access Control sublayer of the Data-Link Layer (DLL) of telecommunication protocols. There is a different MAC sublayer for each physical device type. Layer 3 refers to the network layer of the Open Systems Interconnection (OSI) multilayered communication model. The network layer is concerned with knowing the address of the neighboring nodes in the network, selecting routes and quality of service, and recognizing and forwarding to the transport layer incoming messages for local host domains.
To assist with relaying of packets, each node may maintain routes or routing information to other nodes in the network and can utilize routing techniques to adapt to changes in the interconnectivity between nodes. The nodes can maintain this routing information by performing periodic link and topology updates. Alternatively, nodes may discover routing information only when needed, instead of utilizing updates to maintain routes.
To centralize control some ad hoc networks manually configure one of the nodes as a “root” node. In some cases, the node which is configured as the root node may be one which is directly connected to infrastructure or a wired network. The root node acts as a centralized point of control in such ad hoc networks. Among other functions, the root node can direct requests (e.g., control information) and data traffic to appropriate nodes in the network. One drawback associated with defining or pre-configuring a specific node as the root node is that the root node may not be in an optimal location within the ad hoc network. This can unnecessarily increase messaging as well as delay responses. Moreover, if the root node looses connectivity, then the functionality provided by that root node is lost.
Notwithstanding these advances, there is a need for improved techniques for designating, identifying and/or selecting a root node in an ad hoc network.
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